Process for producing p-hydroxybenzaldehyde

ABSTRACT

A process for producing p-hydroxybenzaldehyde through p-aminobenzaldehyde from p-nitrotoluene, comprising reacting p-nitrotoluene with sodium polysulphide in an alcohol-alkali aqueous solution mixed solvent in the presence or absence of an aprotic polar compound to produce p-aminobenzaldehyde, diazotizing the p-aminobenzaldehyde and then hydrolyzing the diazotized p-aminobenzaldehyde to produce p-hydroxybenzaldehyde.

This is a division of application Ser. No. 938,125, filed Aug. 30, 1978now U.S. Pat. No. 4,195,041.

This invention relates to a process for producing p-hydroxybenzaldehydeand more particularly it relates to a process for producingp-hydroxybenzaldehyde by reacting p-nitrotoluene with sodiumpolysulphide to obtain p-aminobenzaldehyde, diazotizing the thusobtained p-aminobenzaldehyde and hydrolyzing the diazotizedp-aminobenzaldehyde to produce the p-hydroxybenzaldehyde.

P-hydroxybenzaldehyde is useful as an intermediate material formedicines, agricultural chemicals, perfumery and is in increasing demandyear by year. There have heretofore been known many processes such as aReimer-Tiemann process disclosed in U.S. Pat. No. 3,365,500 and aphosphoric acid ester process described in Japanese Patent Gazette No.3828/73. The former process comprises reacting phenol with chloroform inthe presence of an alkali to produce salicylaldehyde andp-hydroxybenzaldehyde; however, the amount of p-hydroxybenzaldehyde soproduced is within the range of as small as 20-25% of the total weightof said two aldehydes and the yield thereof is within the range of15-20% at highest based on the amount of phenol used because the mainproduct contained in the reaction mixture is salicylaldehyde.

On the other hand, the latter process comprises chlorinatingtri-p-cresylphosphate in the presence of an azobis type catalyst such asazobis isobutyronitrile and hydrolyzing the thus chlorinated compound toproduce p-hydroxybenzaldehyde; however, this known process isdisadvantageous in that tri-p-cresylphosphate as the starting materialis an awkward compound to handle industrially because it is solid atambient temperature and that said chlorinated compound takes a long timeto be hydrolyzed because of its low hydrolyzability.

In addition, there have hitherto been known processes for the productionof p-aminobenzaldehyde by reacting p-nitrotoluene with sodiumpolysulphide; for example, Organic Synthesis, Collective, Vol. 4, p. 31describes a process for the production of p-aminobenzaldehyde byreacting p-nitrotoluene with sodium polysulphide prepared byincorporating sodium sulphide with sulphur and further with sodiumhydroxide. However, this known process can only producep-aminobenzaldehyde in a yield of as low as 40-50%.

Diazotization or diazo-reactions, in general, are illustrated in, forexample, Experimental Organic Chemistry (third revised edition) writtenby S. Yamaguchi and published in 1934 by Nankodo Bookstore, Japan, thepublication describing on page 339 thereof a process for the synthesisof guaiacol from o-anisidine by dissolving o-anisidine in iced water andsulphuric acid to form a solution, adding sodium nitrite to the thusformed solution for diazotization of the o-anisidine and thenhydrolyzing the diazotized compound in a mixed liquid, at 135°-140° C.,of conc. sulphuric acid and anhydrous sodium sulphate to obtainguaiacol. Further, Organic Synthesis, Collective Vol. 3, describes onpage 130 thereof a process for the synthesis of 3-bromo-4-hydroxytolueneby diazotizing and hydrolyzing 3-bromo-4-aminotoluene; in this case ahydrolyzing temperature of 130°-135° C. is employed and a possible hightemperature is generally believed to be desirable and, to this end, thehydrolyzing temperature is raised by the addition of sodium sulphate orthe like.

Even if said diazotization and hydrolysis of o-anisidine be applied to aprocess for the production of p-hydroxybenzaldehyde fromp-aminobenzaldehyde, p-hydroxybenzaldehyde will be obtained in a verylow yield. Further, even if the process described in the aforesaidOrganic Synthesis be applied to a process for the production ofp-hydroxybenzaldehyde, the reaction will not satisfactorily proceedwhile producing tarry materials with the result that the desired productis obtained in a low yield as indicated in Comparative example 3 to bedescribed later.

P-aminobenzaldehyde which may be used as a starting material forp-hydroxybenzaldehyde, is a compound which is thermally unstable in anacidic medium. It is easily condensed to form a Schiff's base asindicated in the following reaction formula: ##STR1##

The condensation further proceeds to form the following polymer:##STR2## wherein n is an integer of one or more.

Thus, it is necessary to stabilize p-aminobenzaldehyde by converting itrapidly to its sulphate ##STR3##

Various studies were made by the present inventors in an attempt toproduce p-hydroxybenzaldehyde through p-aminobenzaldehyde fromp-nitrotoluene and, as the result of their studies, it has been foundthat p-hydroxybenzaldehyde may be obtained in a good yield by dissolvingp-nitrotoluene in a mixed solvent of an alcohol and an aqueous alkalisolution, reacting the p-nitrotoluene in solution with sodiumpolysulphide in the presence or absence of an aprotic polar compound toproduce p-aminobenzaldehyde, diazotizing the thus producedp-aminobenzaldehyde and then hydrolyzing the diazotized compound toobtain p-hydroxybenzaldehyde in a good yield. This invention is based onthis finding or discovery.

An object of this invention is to provide a process for producingp-aminobenzaldehyde in a good yield from p-nitrotoluene. This processcomprises reacting p-nitrotoluene with sodium polysulphide (Na₂ Sx)prepared by reacting sodium hydroxide with hydrogen sulphide to formsodium hydrosulphide and incorporating the thus formed sodiumhydrosulphide with sodium hydroxide and then with sulphur.

Another object of this invention is to provide a process for producingp-hydroxybenzaldehyde stably, substantially stoichiometrically andwithout producing tarry materials at the time of hydrolysis, fromp-aminobenzaldehyde which is thermally unstable in an acidic medium. Asmeans for attaining this object, intensive studies were made by thepresent inventors to find the optimum reaction time and temperature usedin the conversion of p-aminobenzaldehyde to the sulphate thereof by theaddition of sulphuric acid and also to find the optimum temperaturerange used in the hydrolysis of the diazonium salt when producingp-hydroxybenzaldehyde from p-aminobenzaldehyde, after which the optimumreaction conditions have been found. Thus, this process comprises addingp-aminobenzaldehyde to an aqueous solution (preferably 2-50 wt.%) ofsulphuric acid at a specified temperature of 60°-100° C., preferably75°-90° C., to form the sulphate thereof as rapidly as possible andhydrolyzing, after cooling, the thus formed sulphate with water or anaqueous solution (preferably, less than 70 wt.% concentration) ofsulphuric acid at a specified temperature of 70°-100° C. to obtainp-hydroxybenzaldehyde under the advantageous conditions as mentionedabove.

Still another object of this invention is to provide a novel process forproducing p-hydroxybenzaldehyde through p-aminobenzaldehyde fromp-nitrotoluene. This process comprises reacting p-nitrotoluene withsodium polysulphide prepared by reacting sodium hydroxide with hydrogensulphide and incorporating the resulting sodium hydrosulphide withsodium hydroxide and then with sulphur, in the presence or absence of anaprotic polar compound in a mixed solvent consisting of an alcohol andan aqueous alkali solution to produce p-aminobenzaldehyde, adding thethus produced p-aminobenzaldehyde to an aqueous solution, preferably a2-50 wt.% aqueous solution of sulphuric acid at 60°-100° C., preferably75°-90° C., to produce the sulphate thereof rapidly, diazotizing (aftercooling) the thus produced sulphate to obtain a diazonium salt ofp-aminobenzaldehyde and then hydrolyzing the thus obtained diazoniumsalt in water or an aqueous solution of sulphuric acid at 70°-100° C. toobtain p-hydroxybenzaldehyde.

In producing p-aminobenzaldehyde by reacting p-nitrotoluene with sodiumpolysulphide according to this invention, the sodium polysulphide maypreferably be a specific one which is prepared by reacting sodiumhydroxide in aqueous solution with hydrogen sulphide to produce sodiumhydrosulphide, adding sodium hydroxide to the thus produced sodiumhydrosulphide to produce sodium sulphide and then adding sulphur to thesodium sulphide so produced, however, the sodium polysulphide does nothave to be limited to the aforesaid specific one. It is preferable thatthe alcohol and the aqueous alkali solution be present in a ratio byweight of 0.1-2:1 in said mixed solvent, that the aqueous alkalisolution contains an alkali in a concentration of 1-50% by weightthereof and that the mixed solvent be used in an amount of 4-100 partsby weight per part by weight of p-nitrotoluene. The concentration of theaqueous solution of sodium hydroxide to be reacted hydrogen sulphide ispreferably in the range of 1-30% by weight. In the production ofp-aminobenzaldehyde, it is preferable that p-nitrotoluene be reactedwith sodium polysulphide in a molar ratio of 2-8:1 at a temperature of50°-120° C. for a time sufficient to produce p-aminobenzaldehyde.

Even if sodium polysulphide prepared by a conventional known method isreacted with p-nitrotoluene in the production of p-aminobenzaldehydefrom p-nitrotoluene, the p-aminobenzaldehyde will be produced in aremarkably increased yield so long as the reaction is effected in thepresence of an aprotic polar compound in an "alcohol-alkali aqueoussolution" mixed solvent according to this invention. Alternatively, theuse of the specific sodium polysulphide according to this invention willresult in producing p-aminobenzaldehyde in an increased yield even ifthe aprotic polar compound is not used in the reaction.

The alcohols which may be used in this invention include methanol,ethanol, ethylene glycol, ethylene glycol monomethyl ether, ethyleneglycol monoethyl ether and mixtures thereof, among which alcoholicmixtures containing at least 80% by weight of ethanol (with theremainder being another alcohol, water or the like, or a mixturethereof) are preferred for increasing the yield of p-aminobenzaldehydeto be obtained.

The aprotic polar compounds used herein include N, N-dimethylformamide,N, N-diethylformamide, N, N-diphenylformamide, dimethylsulfoxide,tris(trimethylamino) phosphate, tetrahydrofuran, acetonitrile and otherpolar compounds which will not liberate H⁺ therefrom. The use of theaprotic polar compound in an amount of 0.01-10% by weight ofp-nitrotoluene will result in producing p-aminobenzaldehyde in aremarkably increased yield. The use thereof in an amount of less than0.01% by weight will be ineffective in increasing the yield and the usethereof in amount of more than 10% by weight will, far from increasingthe yield, decrease it. Among said aprotic polar compounds, N,N-dimethylformamide is particularly preferred.

It is unexpected that the reaction of the specific sodium polysulphideprepared by the previously mentioned new method different fromconventional ones, with p-nitrotoluene will produce p-aminobenzaldehydein a much higher yield (such as 55-60%) than has heretofore beenpossible. Although the mechanism of reaction between p-nitrotoluene andthe specific sodium polysulphide is not clearly known, said much higheryield is considered to be due to delicate differences in chemicalstructure between the specified sodium polysulphide according to thisinvention and the conventional one.

The temperature at which hydrogen sulphide is reacted with sodiumhydroxide in aqueous solution is not particularly limited, but it maypreferably be a comparatively low temperature which is in the range of10°-60° C. The use of lower temperatures will make the reactionprolonged, while the use of higher temperatures will decrease thereaction efficiency of the hydrogen sulphide.

It is desirable that sodium hydroxide be added to the sodiumhydrosulphide obtained in a molar ratio of from 1.0 to 3.0 to producesodium sulphide. The addition of sodium hydroxide in a molar ratio ofless than 1.0 will result in producing p-aminobenzaldehyde in a lowyield, while the addition thereof in a molar ratio of more than 3.0 willnot result in increasing the yield to an appreciable extent, this beingeconomically disadvantageous.

In the production of sodium polysulphide according to this invention bythe addition of sulphur, it is desirable that sulphur be added in suchan amount as to produce a sodium polysulphide represented by the formulaNa₂ Sx wherein x is an integer of from 2 to 5. If sulphur be not addedin such an amount as mentioned above, then by-products will be producedin large amounts and the desired product obtained in a decreased yield.

If the thus obtained sodium polysulphide according to this invention isreacted with p-nitrotoluene in a mixed solvent consisting of an aqueousalkali solution and an alcoholic mixture containing at least 80% byweight of ethanol, then p-aminobenzaldehyde will be obtained in a goodyield.

According to this invention, it is necessary to reactp-aminobenzaldehyde with sulphuric acid to form the sulphate thereof inas short a time as possible by heating said starting reactants to60°-100° C. If p-hydroxybenzaldehyde be attempted to be obtained fromthe sulphate of p-aminobenzaldehyde, whether the reaction for producingthe sulphate of p-aminobenzaldehyde was effected at lower than 60° C.for a long time or at higher than 100° C. for an extremely short time,the sulphate of p-aminobenzaldehyde obtained at the lower reactiontemperature will give p-hydroxybenzaldehyde in a low yield while thatobtained at the higher reaction temperature will disadvantageously givea low yield, accompanied with the formation of tarry materials.

Thus, according to this invention, a sulphuric acid solution andp-aminobenzaldehyde added thereto are reacted together at 60°-100° C.,preferably 75°-90° C., under agitation for 10-30 minutes. The sulphuricacid concentration of the solution is not particularly limited, but itis preferably in the range of usually 2-50% by weight.

The sulphate of p-aminobenzaldehyde so obtained is immediately cooled(to a low temperature such as 10° to 0° C.) by cooled or iced water andthen diazotized with a usual diazotizing agent such as an aqueoussolution of sodium nitrite while adding the agent dropwise to thesulphate so cooled. It is effective or preferable in this case to add tothe thus diazotized compound a decomposing agent, such as sulfamic acidor urea, in such an amount necessary for decomposing an excess of thesodium nitrite added. The diazotizing agents used herein may includesodium nitrite, potassium nitrite, ammonium nitrite and nitrosylsulphuric acid, and they may be used in a concentration of 5-50% byweight at lower than 10° C. in the diazotization.

The diazonium salt of p-aminobenzaldehyde may preferably be hydrolyzedat a temperature in the range of from 70° to 100° C.; if the hydrolysisbe effected at a temperature above 100° C. then tarry materials will beproduced, while if it be effected at a temperature below 70° C. then itwill not proceed smoothly. Therefore, it is necessary in the practice ofthis invention to carry out the hydrolysis at a temperature ranging from70° to 100° C. in water or an aqueous solution of sulphuric acid.

This invention will be better understood by the following Examples andComparative examples wherein all the percentages are by weight unlessotherwise specified.

EXAMPLE 1

A solution of 5 g (0.125 mol) of sodium hydroxide in 10 g of water wasintroduced into a 100 -ml flask, maintained at 45° C. and then reactedwith 4.1 g (0.121 mol) of hydrogen sulphide by passing it through thesolution for one hour, to obtain an aqueous solution of sodiumhydrosulphide. The aqueous solution of sodium hydrosulphide so obtainedwas introduced into a 1-liter flask and incorporated with 9.1 g (0.228mol) of sodium hydroxide and 547 g of water to produce an aqueoussolution of sodium sulphide. The aqueous solution of sodium sulphide soproduced was incorporated with 14.5 g (0.45 mol) and reacted together at80° C. for one hour to produce an aqueous solution of sodiumpolysulphide which was represented by the formula Na₂ Sx wherein x is avalue of 3.

To a 1-liter flask were added 66.7 g (0.487 mol) of p-nitrotoluene, 223g of ethanol and 2.7 g (4.1% by weight of the p-nitrotoluene) of N,N-dimethylformamide to form a mixture which was dissolved, maintained at80° C. and then incorporated dropwise over a period of time of 2 hourswith an aqueous alkali solution prepared by adding 51.5 g of a 50%aqueous solution of sodium hydroxide to said aqueous solution of sodiumpolysulphide. After the end of the incorporation with the aqueous alkalisolution, the whole mass was refluxed for an additional two hoursthereby completing the reaction. The resulting reaction mixture wassubjected to steam distillation to obtain 42.3 g (0.350 mol) ofp-aminobenzaldehyde in purified form. The yield of thep-aminobenzaldehyde so obtained was 71.8%, based on the weight ofp-nitrotoluene used.

To the same 1-liter flask as above were added 292.5 g of a 40% aqueoussolution of sulphuric acid and 42.3 g (0.350 mol) of p-aminobenzaldehydeto form a mixture which was heated to 80° C., reacted at thistemperature under agitation for 15 minutes, soon thereafter incorporatedwith 158.6 g of iced water to cool the resulting reaction mixture. Thereaction mixture so cooled was incorporated dropwise over a time periodof 30 minutes with a solution of 28.2 g (0.41 mol) of sodium nitrite in79.3 g of water while maintaining the solution at a temperature of lowerthan 5° C., incorporated with 2.6 g (0.06 mol) of urea to decompose anexcess of the sodium nitrite used and further incorporated with 529 g oficed water for dilution thereby obtaining 1132 g of an aqueous solutionof a diazonium salt of p-aminobenzaldehyde.

The thus obtained aqueous solution of the diazonium salt maintained atlower than 5° C. was added dropwise over a period of time of 30 minutesto 767 g of a 20% aqueous solution of sulphuric acid heated to 80° C.and, soon after the end of the addition, heated rapidly to 90° C. tocomplete the hydrolysis of the diazonium salt thereby obtaining 43.2 g(0.354 mol) of p-hydroxybenzaldehyde. The yield of the thus obtainedp-hydroxybenzaldehyde was substantially stoichiometric with respect tothe amount of p-aminobenzaldehyde used and was therefore 71.8%, based onthe weight of p-nitrotoluene used.

EXAMPLE 2

The procedure of Example 1 was followed except that 2.3 g (3.4 wt.% ofthe p-nitrotoluene) of acetonitrile were substituted for the N,N-dimethylformamide, to obtain 37.7 g (0.312 mol) of p-aminobenzaldehydeand then obtain 38.5 g (0.315 mol) of p-hydroxybenzaldehyde.

Thus, the yield of the thus obtained p-hydroxyaldehyde was 64.8%, basedon the weight of p-nitrotoluene used.

EXAMPLE 3

The procedure of Example 1 was followed except that 3.2 g (4.8% byweight of the p-nitrotoluene) of dimethylsulfoxide were substituted forthe N,N-dimethylformamide, to obtain 38.3 g (0.317 mol) ofp-aminobenzaldehyde and then 39.1 g (0.320 mol) ofp-hydroxybenzaldehyde. Thus, the yield of the p-hydroxybenzaldehyde was65.8%, based on the weight of p-nitrotoluene used.

EXAMPLE 4

Thirty grams (0.125 mol) of sodium sulphide nonahydrate were dissolvedin 600 g of water, incorporated with 15 g (0.47 mol) of sulphur, reactedtogether at 80° C. for one hour to produce sodium polysulphide, and thenincorporated with 27 g of sodium hydroxide to form an aqueous alkalisolution. The aqueous alkali solution so formed was added dropwise overa period of time of 2 hours to a solution of 50 g (0.36 mol) ofp-nitrotoluene in a mixture of 232 g of ethanol and 4.2 g (8.4% byweight of the p-nitrotoluene) of N,N-dimethylformamide while maintainingsaid solution at 82° C. After the end of addition of the aqueous alkalisolution, the whole mass was refluxed for an additional two hours tocomplete the reaction thereby producing p-aminobenzaldehyde. The amountof the p-aminobenzaldehyde so produced was 27.9 g (0.23 mol) and theyield thereof was 64%, based on the weight of p-nitrotoluene used. Thep-aminobenzaldehyde so produced was diazotized and hydrolyzed in thesame manner as in Example 1 to obtain 28.9 g (0.23 mol) ofp-hydroxybenzaldehyde. The yield of this final product was 64%, based onthe weight of p-nitrotoluene used.

COMPARATIVE EXAMPLE 1

The procedure of Example 1 was followed except that the N,N-dimethylformamide was not added, to obtain p-hydroxybenzaldehyde. Theyield of the p-hydroxybenzaldehyde was 56%, based on the weight ofp-nitrotoluene used.

COMPARATIVE EXAMPLE 2

The procedure of Example 4 was followed except that the N,N-dimethylformamide was not added, to obtain p-hydroxybenzaldehyde in ayield of 40%, based on the weight of p-nitrotoluene used.

COMPARATIVE EXAMPLE 3

The procedure of Example 1 was repeated except that theN,N-dimethylformamide was not added and p-aminobenzaldehyde was reactedwith sulphuric acid in 40% aqueous solution at 40° C. for one hour, toobtain p-hydroxybenzaldehyde in a yield of 23%, based on the weight ofp-nitrotoluene used.

EXAMPLE 5

A solution of 14 g (0.35 mol) of sodium hydroxide in 28 g of water wasintroduced into a 100-ml flask where the solution was maintained at 45°C. and reacted with 10.6 g (0.31 mol) of hydrogen sulphide by passing itthrough said solution for one hour to obtain 52.6 g of an aqueoussolution of sodium hydrosulphide. The sodium hydrosulphide solution soobtained was introduced into a 2-liter flask where it was incorporatedwith 22 g (0.55 mol) of sodium hydroxide and 1435 g of water to obtain1509.6 g of an aqueous solution of sodium sulphide. The aqueous solutionof sodium sulphide so obtained was incorporated with 37.4 g (1.17 mol)of sulphur to react the sulphide with sulphur at 80° C. for one hourthereby obtaining 1547 g of an aqueous solution of sodium polysulphidewhich could be represented by the formula Na₂ Sx wherein x is 3.29. Theaqueous solution of sodium polysulphide so obtained was incorporatedwith 135 g of a 50% aqueous solution of sodium hydroxide to render theformer alkaline.

A solution of 175 g (1.28 mol) of p-nitrotoluene in 590 g of ethanol wascharged into a 3-liter flask, maintained at 82° C. and then incorporateddropwise with the whole of said alkaline aqueous solution of sodiumpolysulphide over a period of time of two hours, after which the wholemass was refluxed for another two hours to complete the reaction. Thereaction mixture so obtained was analyzed by high-speed liquidchromatography and found to comprise 87.4 g (0.72 mol) ofp-aminobenzaldehyde and 9.6 g (0.090 mol) of p-toluidine. The reactionmixture was subjected to steam distillation to distil off the ethanoland p-toluidine, and the p-aminobenzaldehyde was crystallized andfiltered out to obtain 86 g (0.71 mol) of p-aminobenzaldehyde in crystalform. The yield of p-aminobenzaldehyde so obtained was 56%, based on theweight of p-nitrotoluene obtained.

EXAMPLE 6

The procedure of Example 5 was followed except that 23.5 g (0.59 mol) ofsodium hydrosulphide were added to the aqueous solution of sodiumhydrosulphide obtained, to obtain 92.9 g (0.77 mol) ofp-aminobenzaldehyde in a yield of 60% of p-nitrotoluene used.

EXAMPLE 7

The procedure of Example 6 was followed except that a modified ethanolcontaining 10% of methanol was substituted for the ethanol, to obtain88.3 g (0.73 mol) of p-aminobenzaldehyde. The yield ofp-aminobenzaldehyde so obtained was 57%, based on the weight ofp-nitrotoluene used.

COMPARATIVE EXAMPLE 4 (the method as described in the previouslymentioned Organic Synthesis)

A solution of 30 g (0.125 mol) of sodium sulphide nonahydrate in 600 gof water was introduced into a 1-liter flask, incorporated with 15 g(0.47 mol) of sulphur and reacted therewith at 80° C. for one hour toobtain sodium polysulphide in aqueous solution. This sodium polysulphidewas such that it was represented by the formula Na₂ Sx wherein x was4.5. The sodium polysulphide in aqueous solution so obtained wasincorporated with 27 g of sodium hydroxide to obtain an alkaline aqueoussolution which was added dropwise at 82° C. to a solution of 50 g (0.36mol) of p-nitrotoluene in 300 ml of 95% ethanol (the remaining 5% beingsubstantially methanol) over a period of time of 2 hours, after whichthe whole mass was refluxed for 2 hours to complete the reaction. Thereaction mixture thus obtained was subjected to high-speed liquidchromatography and found to contain 18.3 g (0.15 mol) ofp-aminobenzaldehyde and 3.9 g (0.036 mol) of p-toluidine.

The reaction mixture was subjected to steam distillation to distil offthe ethanol and the p-toluidine, and then the p-aminobenzaldehyde wascrystallized and filtered out thereby obtaining 17.4 g (0.14 mol) ofcrystals thereof. The yield of p-amonibenzaldehyde so obtained was 40%,based on the weight of p-nitrotoluene used.

COMPARATIVE EXAMPLE 5

The procedure of Example 5 was followed except that 8 g (0.2 mol) ofsodium hydroxide were added to the 52.6 g of the aqueous solution ofsodium hydrosulphide, to obtain 69.7 g (0.576 mol) ofp-aminobenzaldehyde which was represented by the formula Na₂ Sx whereinx is 5.38.

The yield of p-aminobenzaldehyde so obtained was 45%, based on theweight of p-nitrotoluene used.

EXAMPLE 8

To a 500-ml glass-made reactor provided with an agitator were added 33.2g of a 40% aqueous solution of sulphuric acid and 4.8 g (0.04 mol) ofp-aminobenzaldehyde to form a mixture. The mixture so formed was heatedto 80° C., reacted together under agitation at this temperature for 15minutes, incorporated with 18 g of iced water to cool the resultingreaction mixture rapidly, incorporated dropwise over a time period of 30minutes with a solution of 3.2 g (0.047 mol) of sodium nitrite in 9 g ofwater while maintaining the solution at a temperature below 5° C.,incorporated with 0.3 g (0.005 mol) of urea to decompose an excess ofthe sodium nitrite and then incorporated with 60 g of iced water fordilution thereby to obtain 128.5 g of an aqueous solution of a diazoniumsalt of p-aminobenzaldehyde.

The thus obtained diazonium salt solution maintained at a temperaturebelow 5° C. was added over a period of time of 30 minutes to 87 g of a20% aqueous solution of sulphuric acid heated to 80° C., after which thewhole mass was heated rapidly to 90° C. to complete the hydrolysis ofthe diazonium salt. The thus obtained p-hydroxybenzaldehyde amounted to4.9 g (0.04 mol) and the yield thereof was substantially stoichiometricwith respect of the amount of p-aminobenzaldehyde used.

EXAMPLE 9

The procedure of Example 8 was followed except that 87 g of water wereused in substitution for the 20% aqueous solution of sulphuric acid asthe decomposing liquid, to obtain 4.5 g (0.037 mol) ofp-hydroxybenzaldehyde. The yield thereof was 92%, based on the weight ofp-aminobenzaldehyde used.

COMPARATIVE EXAMPLE 6

The procedure of Example 8 was followed except that the production ofthe sulphate of p-aminobenzaldehyde by reaction with sulphuric acid in40% aqueous solution was effected at 40° C. for one hour, to obtain 2.0g (0.016 mol) of p-hydroxybenzaldehyde. The yield thereof was 41%, basedon the weight of p-aminobenzaldehyde used.

COMPARATIVE EXAMPLE 7

The procedure of Example 8 was followed except that the reaction ofp-aminobenzaldehyde with sulphuric acid in 40% aqueous solution waseffected at 120° C. for 15 minutes, to obtain 2.6 g (0.021 mol) ofp-hydroxybenzaldehyde, accompanied with formation of tarry materials inlarge quantities. The yield of p-hydroxybenzaldehyde so obtained was53%, based on the weight of p-aminobenzaldehyde used.

COMPARATIVE EXAMPLE 8

The procedure of Example 8 was followed except that a mixture of 15 g ofsodium sulphate with 30 g of a 67% aqueous solution of sulphuric acidwas substituted for the 20% aqueous solution of sulphuric acid as thedecomposing liquid and that a hydrolyzing temperature of 130° C. wasused, to obtain 2.0 g (0.016 mol) of p-hydroxybenzaldehyde. The yield ofp-hydroxybenzaldehyde so obtained was 42%, based on the weight ofp-aminobenzaldehyde, and, in this case, tarry materials were produced inlarge quantities.

What is claimed is:
 1. In a process for producing p-aminobenzaldehydefrom p-nitrotoluene comprising reacting p-nitrotoluene with sodiumpolysulphide in a mixed solvent consisting of at least one alcohol andan alkali aqueous solution in the presence of an aprotic polar compoundto produce the p-aminobenzaldehyde.
 2. A process according to claim 1,wherein the at least one alcohol is a member selected from the groupconsisting of methanol, ethanol, ethylene glycol, ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether and mixtures thereof.3. A process according to claim 1, wherein the at least one alcoholcontains at least 80% by weight of ethanol.
 4. A process according toclaim 1, wherein the aprotic polar compound is used in an amount of0.01-10% by weight of p-nitrotoluene.
 5. A process according to claim 1,wherein the aprotic polar compound is a member selected from the groupconsisting of N,N-dimethylformamide, N,N-diethylformamide,N,N-diphenylformamide, dimethylsulfoxide, tris(trimethylamino)phosphate,tetrahydrofuran and acetonitrile.
 6. A process according to claim 1,wherein the sodium polysulphide is represented by the formula Na₂ Sxwherein x is an integer of 2-5.
 7. A process according to claim 5,wherein the sodium polysulphide is represented by the formula Na₂ Sxwherein x is an integer of 2-5.
 8. A process according to claim 1,wherein the sodium polysulphide is one prepared by reacting sodiumhydroxide in aqueous solution with hydrogen sulphide to produce sodiumhydrosulphide, reacting the thus produced sodium hydrosulphide withsodium hydroxide to produce sodium sulphide and then reacting the thusproduced sodium sulphide with sulphur to produce the sodiumpolysulphide.
 9. A process according to claim 8, wherein the reaction ofsodium hydroxide in aqueous solution with hydrogen sulphide is effectedat a temperature of 10°-60° C.
 10. A process according to claim 8,wherein the sodium hydrosulphide is incorporated with the sodiumhydroxide in a molar ratio of 1.0-3.0.
 11. A process for producing adiazonium salt of p-aminobenzaldehyde from p-nitrotoluene comprising thesteps of:reacting p-nitrotoluene with sodium polysulphide in a mixedsolvent consisting of at least one alcohol and an alkali aqueoussolution in the presence of an aprotic polar compound to producep-aminobenzaldehyde, adding the thus produced p-aminobenzaldehyde to anaqueous solution of sulphuric acid at 60°-100° C. to produce thesulphate thereof rapidly, and diazotizing, after cooling, the thusproduced sulphate to produce a diazonium salt of p-aminobenzaldehyde.12. A process according to claim 11, wherein the aqueous solution ofsulphuric acid contains sulphuric acid in a concentration of 2-50% byweight of the solution.